Button knob



FIG. 1 is a top perspective view of a button knob according to the present design;

FIG. 2 is a bottom perspective view of the button knob seen in FIG. 1;

FIG. 3 is a top view of the button knob seen in FIG. 1;

FIG. 4 is a bottom view of the button knob seen in FIG. 1; and,

FIG. 5 is a side view of the button knob seen in FIG. 1. 

CLAIM The ornamental design for a button knob, as shown and described. 